In a large bowl, whisk together the pudding and milk until combined. Set aside.
I used a 9x13 inch Pyrex dish for the cake. You can use a baking dish with the same dimensions. Line the bottom with graham crackers. Add about 1/3 of the pudding and spread. Add another layer of graham crackers over the pudding, then add 1/3 of the pudding on top. Spread to coat. Add a third layer of crackers over the pudding and top with the remaining pudding. Cover and refrigerate for 1 hour.
Top with nuts (or sprinkles or shaved chocolate). Cut into squares and serve.